There are players who were engraved with the Moyes way, tight solid shape, those players then had to try and adapt to Martinez and his possession is everything, defending is nothing approach. These players partially adapted to this in the first season and caught a lot of people by surprise but in time the inevitable happened and Martinez destroyed the defensive mentality and work rate that Moyes put into them. Martinez got in players to suit his 'way' who evidently can't defend and actually couldn't pass keep the ball and the Martinez way was found out big time.
Koeman brought in a couple of players in the summer, one of whom is or should I say was the mould of what he wants, especially the attacking part of the pitch in Bolasie. He obviously wanted more than had been brought in, just look at how ruthless he was with Niasse after just 20 minutes in Austria.
We all know how many players the squad needs binning, regardless of the result we have the same players underperforming consistently.